Recombinant DNA technology can be used to assay types of genetic variability in natural populations that were previously not feasible to study. This proposal is concerned with three related applicants of this new ability. The first is the simultaneous use of paternally (Y-chrosomal DNA), maternally (mitochondrial DNA), and bisexually (ribosomal DNA, single copy nuclear DNA) inherited DNA markers to examine the population structure of certain insect and reptile species (although the analytical framework and experimental protocol will also be applicable to studies of human population structure). Population structure refers to the effective population sizes, systems of mating, and patterns of gene flow that occur within a species. These parameters have a major impact on the amount and distribution of genetic variation within a specie and upon the course of adaptive evolution and speciation. However, the current amount and distribution of genetic variation is also dependent upon past events, and most importantly upon founder and bottleneck events in which the species underwent episodes of small population size in the past. Such bottlenecks are thought to have played a critical role in determining the incidence of genetic disease in certain human populations. Consequently, the second application outlined in this proposal will be the reconstruction of historical founder and bottleneck effects from studies on restriction site polymorphism in mitochondrial and ribosomal DNA. The historical information encoded in the DNA also extends back beyond the history of the species itself, and the third application is the use of recombinant DNA techniques in reconstructing phylogenies of closely related existing species. This phylogenetic information is needed to assess the genetic impact of speciation and to more fully integrate population genetics with macroevolution. Such information will also allow us to test many hypotheses stemming from the area of molecular evolution. In summary, recombinant DNA technology will be used to examine some of the evolutionary forces--both current and historical--that greatly influence the amount and distribution of genetic variation among and between populations and species.